1. Field of Invention
The present invention pertains to perforating guns used in subsurface wells, and particularly to perforating guns having stackable sections.
2. Related Art
It is often desirable to perforate zones of interest in a subterranean well with very long gun strings to maximize production of well fluids, such as hydrocarbons. This is particularly true in horizontal or highly deviated wells. Gun strings may range in length from a few hundred feet to several thousand feet. Perforating guns are often run into the well using coiled tubing, though drill string may be used if a rig is present at the well site.
Generally, it is faster and safer to run and retrieve a gun string in an underbalanced well using coiled tubing. (Underbalanced operations help prevent damage to formations.) If drill string is used, a snubbing unit must also be used to seal and control pressure from well fluids. Though coiled tubing may be faster and safer, its use may limit the length of the gun string because the coiled tubing can only push so much load before its buckling strength is exceeded. This is particularly true in horizontal or nearly horizontal wells.
There are existing systems for downhole stacking of guns. U.S. Pat. No. 6,098,716, assigned to Schlumberger Technology Corporation, is one example. However, those prior art systems have sections that are intended to be stacked in vertical or nearly vertical holes, not horizontal holes. The Schlumberger system uses a connector that mechanically latches in compression, but is not designed to carry a tensile load. Other prior art systems stack, but do not latch at all, and thus can carry neither compressive nor tensile loads. Thus, there is a continuing need for improved sectional perforating guns.